Run engine until normal operating temperature is reached. Remove air cleaner cover and filter element. Disconnect hose from main air jet solenoid valve and install vacuum pump. Start engine and apply vacuum at idle. If no vacuum is present, proceed to step 4).
If vacuum is present, check for voltage at main air jet solenoid valve. If voltage is not present, replace solenoid valve and retest. If there is voltage, continue with test steps.
Check speed sensor (auto. trans. only), intake air temperature sensor and vacuum switch A. Check for voltage at control unit connector (Black/Yellow wire) with ignition on. Voltage should be present. If voltage is not present, check wiring. Ensure Brown/Black wire between control unit and ground has continuity.
Disconnect vacuum hose No. 2 from control box No. 1. Apply vacuum with engine at idle. If vacuum remains constant, disconnect vacuum gauge and reconnect air hoses and air cleaner. If vacuum is not present, check for voltage at main air jet solenoid valve.
If voltage is not present, replace solenoid valve and retest. If there is no voltage, check the following: speed sensor (auto. trans. only), intake air temperature sensor and vacuum switch A. Check for voltage at control unit connector (Black/Yellow wire) with ignition on.
Voltage should be present. If there is no voltage, check wiring. Ensure Brown/Black wire between control unit and ground has continuity.

Fig 1: Main Air Jet Control System

Courtesy of AMERICAN HONDA MOTOR CO., INC.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

System Testing